Bowser Samuel S.

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Bowser
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Samuel S.
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  • Article
    An endobiont-bearing allogromiid from the Santa Barbara Basin : implications for the early diversification of foraminifera
    (American Geophysical Union, 2006-07-19) Bernhard, Joan M. ; Habura, Andrea ; Bowser, Samuel S.
    Our current understanding of paleoecology and paleoceanography is largely based on the superb Phanerozoic fossil record of foraminiferan protists. The early history of the group is unresolved, however, because basal foraminiferans (allogromiids) are unmineralized and thus fossilize poorly. Molecular-clock studies date foraminiferal origins to the Neoproterozoic, but the deep sea – one of Earth’s most extensive habitats and presently a significant fraction of basal foraminiferal diversity— was probably anoxic at that time and, until now, anaerobic allogromiids were unknown. Molecular, cell and ecological analyses reveal the presence of a previously unknown allogromiid inhabiting anoxic, sulfidic deep-sea sediments (Santa Barbara Basin, California, USA). The fact that the new foraminifer harbors prokaryotic endobionts implicates symbiogenesis as a driving force in early foraminiferal diversification.
  • Preprint
    An ectobiont-bearing foraminiferan, Bolivina pacifica, that inhabits microxic pore waters : cell-biological and paleoceanographic insights
    ( 2009-08-17) Bernhard, Joan M. ; Goldstein, Susan T. ; Bowser, Samuel S.
    The presence of tests (shells) in foraminifera could be taken as an indicator that this protist taxon is unlikely to possess ectosymbionts. Here, however, we describe an association between Bolivina pacifica, a foraminiferan with a calcareous test, and a rod-shaped microbe (bacterium or archaeon) that is directly associated with the pores of the foraminiferan’s test. In addition to these putative ectosymbionts, B. pacifica has previously undescribed cytoplasmic plasma membrane invaginations (PMIs). These adaptations (i.e., PMIs, ectobionts), along with the clustering of mitochondria under the pores and at the cell periphery, suggest active exchange between the host and ectobiont. The B. pacifica specimens examined were collected from sediments overlain by oxygen-depleted bottom waters (0.7 μM) of the Santa Barbara Basin (SBB; California, USA). An ultrastructural comparison between B. pacifica from the SBB and a congener (Bolivina cf. B. lanceolata) collected from well-oxygenated sediments (Florida Keys) suggests that PMIs, ectobionts, and peripherally distributed mitochondria are all factors that promote inhabitation of microxic environments by B. pacifica. The calcitic δ13C signatures of B. pacifica and a of co-occurring congener (B. argentea) that lacks ectobionts differ by >1.5‰, raising the possibility that the presence of ectobionts can affect incorporation of paleoceanographic proxies.